Why is there mold in my house? [Updated 2022]

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Three factors must be present for mold to grow and thrive in your home. When the combination of these factors exists in the right proportions, you may start to see or feel the presence of unwanted fungal growth. The issue should be addressed immediately for the health of your family and home.

Mold growth on roof deck


So, What Causes Mold To Grow In Your House?

It’s pretty basic stuff; oxygen, moisture, and food. We know that oxygen is present and we aren’t going to try to change that. Food is present in the form of sheetrock, so that needs to stay. But we can eliminate the moisture.

You may be wondering where this moisture is coming from. 2 rules apply here


1) Moisture moves from warm to cold

The air inside the home is warmer and holding more water molecules than the air outside of the house. Because of rules #1 and #2, the air will travel through the wall. This process is known as vapor diffusion. When the warm moist air meets the cold air within the building envelope, condensation occurs. Voilà, moisture is now present, and fungal growth may kick in.


2) Moisture moves from more to less.

In winter months, warm moist air is generated from everyday activities like breathing, cooking, and boiling water. 

Look at the thermal camera image below. Do you notice the blue and red colors present? Blue represents cold air while red areas show warm air. This means that warm moist air is meeting cool air in the building envelope leaving your home victim to potential moisture, rot, and mold issues. The home in this picture was suffering greatly from the moisture problem.

To stop mold growth and the deterioration of your home, we need to eliminate the presence of water resulting from warm air meeting cold. Complete Building Solutions has over 80 years of collaborative experience in building performance. We design solutions to create and maintain healthy homes.

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